The present invention relates to packaging material, preferably in the form of tubes, suitable for the manufacture of sausage casings and to a process for preparing such material. More especially, the invention relates to the production of tubes having a base layer principally of regenerated cellulose and having a strongly adhering surface layer, preferably on the inside of the tube, which is comprised of a vinylidene chloride-containing copolymer and is substantially impermeable to water vapor, oxygen and flavor substances. Furthermore, the invention pertains to synthetic sausage casings as well as to shirred tubing produced from the packaging material for use in sausage manufacture.
Tubes made of the package material according to the invention are particularly well suited for the manufacture of shirred sausage casings which find utility in the sausage manufacturing industry and as synthetic sausage casings.
Tubes which are commercially utilized as synthetic sausage casings are those based upon cellulose hydrate and these tubes generally have on either their inside or outside surface as coating layer of a vinylidene chloride-containing copolymer. These tubes are available either as rolls or as individual units having one end already closed up. Cellulose hydrate tubes which are suitable for use as synthetic sausage casings and which do not contain any barrier layer coating on their surface have for many years been gathered up or shirred by means of machines which are suitable and well known for this procedure. The procedure is carried out by pleating the tubes in a longitudinal direction into hollow rod-shaped structures. These structures shall be referred to hereinafter as shirred casings. The procedure for producing the shirred casings is known under the designation of shirring or gathering.
These shirred casings are then filled with a sausage mixture by means of any known type of sausage filling machine, wherein the sausage filling recipe is stuffed into the shirred casing which is closed at one end, whereby the shirred casing is continuously unfolded and extended.
It is not possible, however, to carry out this rational process with the known types of tubes which are made from cellulose hydrate and which have a barrier layer coating formed from a polyvinylidene chloride-containing copolymer, since tubes of this type may not be gathered or shirred without causing damage to the shirred casings. In particular, these tubes are not capable of withstanding the strong mechanical stresses which are caused during the shirring procedure. Mechanical stress on the tube takes place above all in the area of the creases produced at the fold in the tube during production of the shirred casings. In these regions, the coating on the tube is damaged. This leads to an uncontrollable and undesirably high permeability of the coating with respect to water vapor, oxygen and also flavor substances, as a result of which the stability and the quality of the sausage are influenced considerably in a disadvantageous manner. Experience shows that the disadvantageous effect of the mechanical action during shirring with this type of tubes generally does not begin immediately after the shirring procedure, but instead renders its effect only after the passage of some time following the processing step.